This invention relates to an electronic typewriter having a correction memory for storing printing data while printing is executed.
In prior art electronic typewriters with a correction function, printing data such as character data and feed data are stored in a correction memory provided in a control section while the characters are printed. The character data are generated in response to the operation of respective character keys and a feed code data is generated in response to the operation of a subscript key (or a paper fore feed key) or a superscript key (or a paper back feed key). The printing paper is fed by a half line spacing responsive to one feed code data by the feed mechanism of the typewriter and henceforth the half line spacing is counted as one unit.
For example, characters "ABCDEF" are printed on a printing paper after the carriage is returned to the left margin position, the subscript key is operated three times and characters "GHIJ" are then printed as shown in FIG. 10. These character code data and the feed code data are stored in the correction memory in that order. When a backspace key (or a backward key) is consecutively operated after the end of the printing of characters "GHIJ", the print head on the carriage retraces the printed line of "GHIJ" backward. The printing paper is reversely fed by the feed code stored in the correction memory and then again retraces the characters in the first printed line (as shown by a solid line in FIG. 10). After the desired position is acquired by the backspace key operations, the operator presses a correction key provided on the keyboard. The printed character at the position is removed, or erased, by the correction mechanism using the corresponding character data stored in the correction memory. The print data stored in the correction memory are cleared when a return key is operated.
The prior art electronic typewriters acting as described above are especially useful in correcting a printed line with superscripted or subscripted characters. The superscripted or subscripted characters are easily erased without requiring the operator to be concerned with paper feed operation.
However, when the feed key is operated a lot of times, it is usually the case that the operator need not retrace to the first line. For example in the FIG. 10, it is more often the case that the operator desires to print in the region 70, shown by a dot line box, when the backspace key is operated. The prior art typewriters have a problem when printing is required within the region, which is one line or more fed from the line of "ABCDEF", after the printing OF "A" through "J" is accomplished. In this case, if the backspace key is operated, the print head retraces the print backward to the position of the first printed line (e.g., at "A" in FIG. 10). Namely, the print head cannot be moved to the region 70 with only the backspace key, but other key operations are required.